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<pre>
IP Security Maintenance and Extensions                        T. Kivinen
(ipsecme)                                                      AuthenTec
Internet-Draft                                           October 1, 2012
Intended status: Informational
Expires: April 4, 2013


                             <span class="h1">Minimal IKEv2</span>
               <span class="h1">draft-kivinen-ipsecme-ikev2-minimal-01.txt</span>

Abstract

   This document describes minimal version of the Internet Key Exchange
   version 2 (IKEv2) protocol.  IKEv2 is a component of IPsec used for
   performing mutual authentication and establishing and maintaining
   Security Associations (SAs).  IKEv2 includes several optional
   features, which are not needed in minimal implementations.  This
   document describes what is required from the minimal implementation,
   and also describes various optimizations which can be done.  The
   protocol described here is compliant with full IKEv2 with exception
   that this document only describes shared secret authentication (IKEv2
   requires support for certificate authentication in addition to shared
   secret authentication).

   This document does not update or modify <a href="./rfc5996">RFC 5996</a>, but provides more
   compact description of the minimal version of the protocol.  If this
   document and <a href="./rfc5996">RFC 5996</a> conflicts then <a href="./rfc5996">RFC 5996</a> is the authoritative
   description.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of <a href="./bcp78">BCP 78</a> and <a href="./bcp79">BCP 79</a>.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at <a href="http://datatracker.ietf.org/drafts/current/">http://datatracker.ietf.org/drafts/current/</a>.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 4, 2013.

Copyright Notice




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   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to <a href="./bcp78">BCP 78</a> and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in <a href="#section-4">Section 4</a>.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.



























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Table of Contents

   <a href="#section-1">1</a>.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  <a href="#page-4">4</a>
     <a href="#section-1.1">1.1</a>.  Use Cases  . . . . . . . . . . . . . . . . . . . . . . . .  <a href="#page-4">4</a>
   <a href="#section-2">2</a>.  Exchanges  . . . . . . . . . . . . . . . . . . . . . . . . . .  <a href="#page-6">6</a>
     <a href="#section-2.1">2.1</a>.  Initial Exchange . . . . . . . . . . . . . . . . . . . . .  <a href="#page-6">6</a>
     <a href="#section-2.2">2.2</a>.  Other Exchanges  . . . . . . . . . . . . . . . . . . . . . <a href="#page-11">11</a>
     <a href="#section-2.3">2.3</a>.  Generating Keying Material . . . . . . . . . . . . . . . . <a href="#page-12">12</a>
   <a href="#section-3">3</a>.  Conformance Requirements . . . . . . . . . . . . . . . . . . . <a href="#page-14">14</a>
   <a href="#section-4">4</a>.  Security Considerations  . . . . . . . . . . . . . . . . . . . <a href="#page-15">15</a>
   <a href="#section-5">5</a>.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . <a href="#page-16">16</a>
   <a href="#section-6">6</a>.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-17">17</a>
   <a href="#section-7">7</a>.  References . . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-18">18</a>
     <a href="#section-7.1">7.1</a>.  Normative References . . . . . . . . . . . . . . . . . . . <a href="#page-18">18</a>
     <a href="#section-7.2">7.2</a>.  Informative References . . . . . . . . . . . . . . . . . . <a href="#page-18">18</a>
   <a href="#appendix-A">Appendix A</a>.  Header and Payload Formats  . . . . . . . . . . . . . <a href="#page-19">19</a>
     <a href="#appendix-A.1">A.1</a>.  The IKE Header . . . . . . . . . . . . . . . . . . . . . . <a href="#page-19">19</a>
     <a href="#appendix-A.2">A.2</a>.  Generic Payload Header . . . . . . . . . . . . . . . . . . <a href="#page-21">21</a>
     <a href="#appendix-A.3">A.3</a>.  Security Association Payload . . . . . . . . . . . . . . . <a href="#page-22">22</a>
       <a href="#appendix-A.3.1">A.3.1</a>.  Proposal Substructure  . . . . . . . . . . . . . . . . <a href="#page-24">24</a>
       <a href="#appendix-A.3.2">A.3.2</a>.  Transform Substructure . . . . . . . . . . . . . . . . <a href="#page-25">25</a>
       <a href="#appendix-A.3.3">A.3.3</a>.  Valid Transform Types by Protocol  . . . . . . . . . . <a href="#page-27">27</a>
       <a href="#appendix-A.3.4">A.3.4</a>.  Transform Attributes . . . . . . . . . . . . . . . . . <a href="#page-28">28</a>
     <a href="#appendix-A.4">A.4</a>.  Key Exchange Payload . . . . . . . . . . . . . . . . . . . <a href="#page-28">28</a>
     <a href="#appendix-A.5">A.5</a>.  Identification Payloads  . . . . . . . . . . . . . . . . . <a href="#page-29">29</a>
     <a href="#appendix-A.6">A.6</a>.  Certificate Payload  . . . . . . . . . . . . . . . . . . . <a href="#page-30">30</a>
     <a href="#appendix-A.7">A.7</a>.  Certificate Request Payload  . . . . . . . . . . . . . . . <a href="#page-31">31</a>
     <a href="#appendix-A.8">A.8</a>.  Authentication Payload . . . . . . . . . . . . . . . . . . <a href="#page-32">32</a>
     <a href="#appendix-A.9">A.9</a>.  Nonce Payload  . . . . . . . . . . . . . . . . . . . . . . <a href="#page-33">33</a>
     <a href="#appendix-A.10">A.10</a>. Notify Payload . . . . . . . . . . . . . . . . . . . . . . <a href="#page-33">33</a>
       <a href="#appendix-A.10.1">A.10.1</a>. Notify Message Types . . . . . . . . . . . . . . . . . <a href="#page-34">34</a>
     <a href="#appendix-A.11">A.11</a>. Traffic Selector Payload . . . . . . . . . . . . . . . . . <a href="#page-35">35</a>
       <a href="#appendix-A.11.1">A.11.1</a>. Traffic Selector . . . . . . . . . . . . . . . . . . . <a href="#page-37">37</a>
     <a href="#appendix-A.12">A.12</a>. Encrypted Payload  . . . . . . . . . . . . . . . . . . . . <a href="#page-38">38</a>
   <a href="#appendix-B">Appendix B</a>.  Useful Optional Features  . . . . . . . . . . . . . . <a href="#page-41">41</a>
     <a href="#appendix-B.1">B.1</a>.  IKE SA Delete Notification . . . . . . . . . . . . . . . . <a href="#page-41">41</a>
     <a href="#appendix-B.2">B.2</a>.  Raw RSA keys . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-42">42</a>
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-44">44</a>













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<span class="h2"><a class="selflink" name="section-1" href="#section-1">1</a>.  Introduction</span>

   This document tells what minimal IKEv2 implementation could look
   like.  Minimal IKEv2 implementation only supports initiator end of
   the protocol.  It only supports the initial IKE_SA_INIT and IKE_AUTH
   exchanges and does not initiate any other exchanges.  It also replies
   with empty (or error) message to all incoming requests.

   This means that most of the optional features of IKEv2 are left out:
   NAT Traversal, IKE SA rekey, Child SA Rekey, Multiple Child SAs,
   Deleting Child / IKE SAs, Configuration payloads, EAP authentication,
   COOKIEs etc.

   Some optimizations can be done because of limited set of supported
   features, and this text should not be considered for generic IKEv2
   implementations (for example Message IDs can be done as specified as
   implementation is only sending out IKE_SA_INIT and IKE_AUTH request,
   and do not ever send any other request).

   This document should be stand-alone, meaning everything needed to
   implement IKEv2 is copied here except the description of the
   cryptographic algorithms.  The IKEv2 specification has lots of
   background information and rationale which has been omitted from this
   document.

   Numerous additional numeric values from IANA registries have been
   omitted from this document, only those which are of interest for
   minimal implementation are listed in this document.

   For more information check the full IKEv2 specification in <a href="./rfc5996">RFC 5996</a>
   [<a href="./rfc5996" title="&quot;Internet Key Exchange Protocol Version 2 (IKEv2)&quot;">RFC5996</a>] and [<a href="#ref-IKEV2IANA">IKEV2IANA</a>].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [<a href="./rfc2119" title="&quot;Key words for use in RFCs to Indicate Requirement Levels&quot;">RFC2119</a>].

<span class="h3"><a class="selflink" name="section-1.1" href="#section-1.1">1.1</a>.  Use Cases</span>

   One use case for this kind of minimal implementation is in small
   devices doing machine to machine communication.  In such environments
   the node initiating connections is usually very small and the other
   end of the communication channel is some kind of larger device.

   An example of the small initiating node could be an remote garage
   door opener device.  I.e. device having buttons which open and close
   garage door, and which connects to the home area network server over
   wireless link.




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   Another example of the such device is some kind of sensor device, for
   example room temperature sensor, which sends periodic temperature
   data to some centralized node.

   Those devices are usually sleeping long times, and only wakes up
   because of user interaction or periodically.  The data transfer is
   always initiated from the sleeping node and after they send packets
   there might be ACKs or other packets coming back before they go back
   to sleep.  If some data needs to be transferred from server node to
   the small device, it can be implemented by polling, i.e. small node
   periodically polls for the server to see if it for example have some
   configuration changes or similar.







































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<span class="h2"><a class="selflink" name="section-2" href="#section-2">2</a>.  Exchanges</span>

<span class="h3"><a class="selflink" name="section-2.1" href="#section-2.1">2.1</a>.  Initial Exchange</span>

   All IKEv2 communications consist of pairs of messages: a request and
   a response.  The pair is called an "exchange", and is sometimes
   called a "request/response pair".  Every request requires a response.

   For every pair of IKEv2 messages, the initiator is responsible for
   retransmission in the event of a timeout.  The responder MUST never
   retransmit a response unless it receives a retransmission of the
   request.

   IKEv2 is a reliable protocol: the initiator MUST retransmit a request
   until it either receives a corresponding response or deems the IKE SA
   to have failed.  A retransmission from the initiator MUST be bitwise
   identical to the original request.  Retransmission times MUST
   increase exponentially.

   IKEv2 is run over UDP port 500.  All IKEv2 implementations MUST be
   able to send, receive, and process IKEv2 messages that are up to 1280
   octets long.  An implementation MUST accept incoming requests even if
   the source port is not 500, and MUST respond to the address and port
   from which the request was received.

   The minimal implementation of IKEv2 only uses first two exchanges
   called IKE_SA_INIT and IKE_AUTH.  Those are used to create the IKE SA
   and the first child SA.  In addition to those messages minimal IKEv2
   implementation need to understand CREATE_CHILD_SA request so it can
   reply with CREATE_CHILD_SA error response saying NO_ADDITIONAL_SAS to
   it, and understand INFORMATIONAL request so much, it can reply with
   empty INFORMATIONAL response to it.  There is no requirement to be
   able to respond to any other requests.

   All messages following the IKE_SA_INIT exchange are cryptographically
   protected using the cryptographic algorithms and keys negotiated in
   the IKE_SA_INIT exchange.

   Every IKEv2 message contains a Message ID as part of its fixed
   header.  This Message ID is used to match up requests and responses,
   and to identify retransmissions of messages.

   Minimal implementation need only support of being initiator, so it
   does not ever need to send any other request as one IKE_SA_INIT, and
   one IKE_AUTH message.  As those messages have fixed Message IDs (0
   and 1) it does not need to keep track of its own Message IDs for
   outgoing requests after that.




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   Minimal implementations can also optimize Message ID handling of the
   incoming requests, as they do not need to protect incoming requests
   against replays.  This is possible because minimal implementation
   will only return error or empty notifications replies to incoming
   requests.  This means that any of those incoming requests do not have
   any effect on the minimal implementation, thus processing them again
   does not cause any harm.  Because of this the minimal implementation
   can always answer to request coming in, with the same Message ID than
   what the request had and then forget the request/response pair
   immediately.  This means there is no need to keep any kind of track
   of Message IDs of the incoming requests.

   In the following descriptions, the payloads contained in the message
   are indicated by names as listed below.

   Notation    Payload
   -----------------------------------------
   AUTH        Authentication
   CERTREQ     Certificate Request
   D           Delete
   HDR         IKE header (not a payload)
   IDi         Identification - Initiator
   IDr         Identification - Responder
   KE          Key Exchange
   Ni, Nr      Nonce
   N           Notify
   SA          Security Association
   SK          Encrypted and Authenticated
   TSi         Traffic Selector - Initiator
   TSr         Traffic Selector - Responder

   The initial exchanges are as follows:

   Initiator                         Responder
   -------------------------------------------------------------------
   HDR(SPIi=xxx, SPIr=0, IKE_SA_INIT,
       Flags: Initiator, Message ID=0),
       SAi1, KEi, Ni  --&gt;

                      &lt;--  HDR(SPIi=xxx, SPIr=yyy, IKE_SA_INIT,
                               Flags: Response, Message ID=0),
                               SAr1, KEr, Nr, [CERTREQ]

   HDR contains the Security Parameter Indexes (SPIs), version numbers,
   and flags of various sorts.  Each endpoint chooses one of the two
   SPIs and MUST choose them so as to be unique identifiers of an IKE
   SA.  An SPI value of zero is special: it indicates that the remote
   SPI value is not yet known by the sender.



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   Incoming IKEv2 packets are mapped to an IKE SA only using the
   packet's SPI, not using (for example) the source IP address of the
   packet.

   The SAi1 payload states the cryptographic algorithms the initiator
   supports for the IKE SA.  The KEi and KEr payload contain Diffie-
   Hellman values and Ni and Nr are the nonces.  The SAr1 contains
   chosen cryptographic suite from initiator's offered choices.  Minimal
   implementation using shared secrets will ignore the CERTREQ payload.

   Minimal implementation will most likely support exactly one set of
   cryptographic algorithms, meaning the SAi1 payload will be static.
   It needs to check that the SAr1 received matches the proposal it
   sent.

   At this point in the negotiation, each party can generate SKEYSEED,
   from which all keys are derived for that IKE SA.

   SKEYSEED = prf(Ni | Nr, g^ir)

   {SK_d | SK_ai | SK_ar | SK_ei | SK_er | SK_pi | SK_pr }
                   = prf+ (SKEYSEED, Ni | Nr | SPIi | SPIr )

   prf+ (K,S) = T1 | T2 | T3 | T4 | ...

   where:
   T1 = prf (K, S | 0x01)
   T2 = prf (K, T1 | S | 0x02)
   T3 = prf (K, T2 | S | 0x03)
   T4 = prf (K, T3 | S | 0x04)
   ...

   (indicating that the quantities SK_d, SK_ai, SK_ar, SK_ei, SK_er,
   SK_pi, and SK_pr are taken in order from the generated bits of the
   prf+). g^ir is the shared secret from the ephemeral Diffie-Hellman
   exchange. g^ir is represented as a string of octets in big endian
   order padded with zeros if necessary to make it the length of the
   modulus.  Ni and Nr are the nonces, stripped of any headers.

   The SK_d is used for deriving new keys for the Child SAs.  The SK_ai
   and SK_ar are used as a key to the integrity protection algorithm for
   authenticating the component messages of subsequent exchanges.  The
   SK_ei and SK_er are used for encrypting (and of course decrypting)
   all subsequent exchanges.  The SK_pi and SK_pr are used when
   generating an AUTH payload.  The lengths of SK_d, SK_pi, and SK_pr
   MUST be the preferred key length of the PRF agreed upon.

   A separate SK_e and SK_a is computed for each direction.  The keys



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   used to protect messages from the original initiator are SK_ai and
   SK_ei.  The keys used to protect messages in the other direction are
   SK_ar and SK_er.  The notation SK { ... } indicates that these
   payloads are encrypted and integrity protected using that direction's
   SK_e and SK_a.

   Initiator                         Responder
   -------------------------------------------------------------------
   HDR(SPIi=xxx, SPIr=yyy, IKE_AUTH,
       Flags: Initiator, Message ID=1),
       SK {IDi, AUTH, SAi2, TSi, TSr,
           N(INITIAL_CONTACT)}  --&gt;

                     &lt;--  HDR(SPIi=xxx, SPIr=yyy, IKE_AUTH, Flags:
                                 Response, Message ID=1),
                                 SK {IDr, AUTH, SAr2, TSi, TSr}

   The initiator asserts its identity with the IDi payload, proves
   knowledge of the secret corresponding to IDi and integrity protects
   the contents of the first message using the AUTH payload.  The
   responder asserts its identity with the IDr payload, authenticates
   its identity and protects the integrity of the second message with
   the AUTH payload.

   As minimal implementation usually has only one host where it
   connects, and that means it has only one shared secret.  This means
   it does not need to care about IDr payload that much.  If the other
   end sends AUTH payload which initiator can verify using the shared
   secret it has, then it knows the other end is the peer it was
   configured to talk to.

   In the IKE_AUTH initiator sends SA offer(s) in the SAi2 payload, and
   the proposed Traffic Selectors for the proposed Child SA in the TSi
   and TSr payloads.  The responder replies with the accepted offer in
   an SAr2 payload, and selected Traffic Selectors.  The selected
   Traffic Selectors may be a subset of what the initiator proposed.

   In the minimal implementation both SA payloads and TS payloads are
   going to be mostly static.  The SA payload will have the SPI value
   used in the ESP, but the algorithms are most likely going to be the
   one and only supported set.  The TS payloads on the initiator end
   will most likely say from any to any, i.e. full wildcard ranges, or
   from the local IP to the remote IP.  In the wildcard case the server
   quite often narrow the range down to the one IP address pair.  Using
   single IP address pair as a traffic selectors when sending IKE_AUTH
   will simplify processing as then server will either accept that pair
   or return error.  If wildcard ranges are used, there is possibility
   that server narrows the range to some other range than what was



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   intended.

   The IKE_AUTH (and IKE_SA_INIT) responses may contain multiple status
   notification payloads which can be ignored by minimal implementation.
   There can also be Vendor ID, Certificate, Certificate Request or
   Configuration payloads, but any payload unknown to minimal
   implementation can simply be skipped over (response messages cannot
   have critical unsupported payloads).

   The exchange above includes N(INITIAL_CONTACT) notification in the
   request as that is quite commonly sent by the minimal implementation.
   It indicates to the other end that the initiator does not have any
   other IKE SAs between them, and if there is any left from previous
   runs they can be deleted.  As minimal implementation does not delete
   IKE SAs by sending IKE SA delete, this will help server to clean up
   leftover state.

   When using shared secret authentication, the peers are authenticated
   by having each calculating a MAC over a block of data:

   For the initiator:
      AUTH = prf( prf(Shared Secret, "Key Pad for IKEv2"),
                       &lt;InitiatorSignedOctets&gt;)
   For the responder:
      AUTH = prf( prf(Shared Secret, "Key Pad for IKEv2"),
                       &lt;ResponderSignedOctets&gt;)

   The string "Key Pad for IKEv2" is 17 ASCII characters without null
   termination.  The implementation can precalculate the inner prf and
   only store the output of it.  This is possible because minimal IKEv2
   implementation usually only supports one PRF.

   The initiator signs the first message (IKE_SA_INIT request), starting
   with the first octet of the first SPI in the header and ending with
   the last octet of the last payload in that first message.  Appended
   to this (for purposes of computing the signature) are the responder's
   nonce Nr, and the value prf(SK_pi, IDi').

   For the responder, the octets to be signed start with the first octet
   of the first SPI in the header of the second message (IKE_SA_INIT
   response) and end with the last octet of the last payload in that
   second message.  Appended to this are the initiator's nonce Ni, and
   the value prf(SK_pr, IDr').

   In these calculations, IDi' and IDr' are the entire ID payloads
   excluding the fixed header and the Ni, and Nr are only the value, not
   the payload containing it.  Note that neither the nonce Ni/Nr nor the
   value prf(SK_pr, IDr')/prf(SK_pi, IDi') are transmitted.



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   The initiator's signed octets can be described as:

   InitiatorSignedOctets = RealMessage1 | NonceRData | MACedIDForI
   GenIKEHDR = [ four octets 0 if using port 4500 ] | RealIKEHDR
   RealIKEHDR =  SPIi | SPIr |  . . . | Length
   RealMessage1 = RealIKEHDR | RestOfMessage1
   NonceRPayload = PayloadHeader | NonceRData
   InitiatorIDPayload = PayloadHeader | RestOfInitIDPayload
   RestOfInitIDPayload = IDType | RESERVED | InitIDData
   MACedIDForI = prf(SK_pi, RestOfInitIDPayload)

   The responder's signed octets can be described as:

   ResponderSignedOctets = RealMessage2 | NonceIData | MACedIDForR
   GenIKEHDR = [ four octets 0 if using port 4500 ] | RealIKEHDR
   RealIKEHDR =  SPIi | SPIr |  . . . | Length
   RealMessage2 = RealIKEHDR | RestOfMessage2
   NonceIPayload = PayloadHeader | NonceIData
   ResponderIDPayload = PayloadHeader | RestOfRespIDPayload
   RestOfRespIDPayload = IDType | RESERVED | RespIDData
   MACedIDForR = prf(SK_pr, RestOfRespIDPayload)

   Note that all of the payloads inside the RestOfMessageX are included
   under the signature, including any payload types not listed in this
   document.

   The initiator might also get unauthenticated response back having
   notification payload with error code inside.  As that error code will
   be unauthenticated and may be faked, there is no need to do anything
   for those.  Minimal implementation can simply ignore those errors,
   and retransmit its request until it times out and if that happens
   then the IKE SA (and Child SA) creation failed.

   Responder might also reply with IKE_AUTH response packet which do not
   contain payloads needed to set up Child SA (SAr2, TSi and TSr), but
   contains AUTH payload and an error.  As minimal implementation
   probably do not support multiple SAs nor sending the CREATE_CHILD_SA
   exchanges the IKE SA is useless for initiator.  It can delete the IKE
   SA and start over from the beginning (which might fail again if this
   is configuration error, or it might succeed if this was temporal
   failure).

<span class="h3"><a class="selflink" name="section-2.2" href="#section-2.2">2.2</a>.  Other Exchanges</span>

   Minimal implementation MUST be able to reply to INFORMATIONAL request
   by sending empty response back:





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   Initiator                         Responder
   -------------------------------------------------------------------
                      &lt;--  HDR(SPIi=xxx, SPIr=yyy, INFORMATIONAL,
                                  Flags: none,  Message ID=m),
                                  SK {...}

   HDR(SPIi=xxx, SPIr=yyy, INFORMATIONAL,
       Flags: Initiator | Response,
       Message ID=m),
       SK {}  --&gt;

   Minimal implementation also MUST be able to reply to incoming
   CREATE_CHILD_SA requests.  Typical implementation will reject the
   CREATE_CHILD_SA exchanges by sending NO_ADDITIONAL_SAS error notify
   back:

   Initiator                         Responder
   -------------------------------------------------------------------
                      &lt;--  HDR(SPIi=xxx, SPIy=yyy, CREATE_CHILD_SA,
                                  Flags: none, Message ID=m),
                                  SK {...}

   HDR(SPIi=xxx, SPIr=yyy, CREATE_CHILD_SA,
       Flags: Initiator | Response, Message ID=m),
       SK {N(NO_ADDITIONAL_SAS)}  --&gt;

   Note, that INFORMATIONAL and CREATE_CHILD_SA requests might contain
   unsupported critical payloads, in which case complient implementation
   MUST ignore the request, and send response message back having the
   UNSUPPORTED_CRITICAL_PAYLOAD notification.  That notification payload
   data contains one-octet payload type of the unsupported critical
   payload.

<span class="h3"><a class="selflink" name="section-2.3" href="#section-2.3">2.3</a>.  Generating Keying Material</span>

   Keying material for Child SA created by the IKE_AUTH exchange is
   generated as follows:

   KEYMAT = prf+(SK_d, Ni | Nr)

   Where Ni and Nr are the nonces from the IKE_SA_INIT exchange.

   A single CHILD_SA negotiation may result in multiple Security
   Associations.  ESP and AH SAs exist in pairs (one in each direction),
   so two SAs are created in a single Child SA negotiation for them.
   The keying material for each Child SA MUST be taken from the expanded
   KEYMAT using the following rules:




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   o  All keys for SAs carrying data from the initiator to the responder
      are taken before SAs going from the responder to the initiator.

   o  If an IPsec protocol requires multiple keys, the order in which
      they are taken from the SA's keying material needs to be described
      in the protocol's specification.  For ESP and AH, [IPSECARCH]
      defines the order, namely: the encryption key (if any) MUST be
      taken from the first bits and the integrity key (if any) MUST be
      taken from the remaining bits.

   Each cryptographic algorithm takes a fixed number of bits of keying
   material specified as part of the algorithm, or negotiated in SA
   payloads.






































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<span class="h2"><a class="selflink" name="section-3" href="#section-3">3</a>.  Conformance Requirements</span>

   For an implementation to be called conforming to <a href="./rfc5996">RFC 5996</a>
   specification, it MUST be possible to configure it to accept the
   following:

   o  Public Key Infrastructure using X.509 (PKIX) Certificates
      containing and signed by RSA keys of size 1024 or 2048 bits, where
      the ID passed is any of ID_KEY_ID, ID_FQDN, ID_RFC822_ADDR, or
      ID_DER_ASN1_DN.

   o  Shared key authentication where the ID passed is any of ID_KEY_ID,
      ID_FQDN, or ID_RFC822_ADDR.

   o  Authentication where the responder is authenticated using PKIX
      Certificates and the initiator is authenticated using shared key
      authentication.

   This document only supports the second bullet, it does not support
   PKIX certificates at all.  As full <a href="./rfc5996">RFC5996</a> responders must also
   support that shared key authentication, this allows minimal
   implementation to be able to interoperate with all <a href="./rfc5996">RFC 5996</a> compliant
   implementations.

   PKIX certificates are left out from the minimal implementation as
   those would add quite a lot of complexity to the implementation.  The
   actual code changes needed in the IKEv2 protocol are small, but the
   certificate validation code would be more complex than the whole
   minimal IKEv2 implementation itself.  If public key based
   authentication is needed for scalability reasons, then raw RSA keys
   would probably be the best compromize (see <a href="#appendix-B.2">Appendix B.2</a>).




















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<span class="h2"><a class="selflink" name="section-4" href="#section-4">4</a>.  Security Considerations</span>

   As this implements same protocol as <a href="./rfc5996">RFC 5996</a> this means all security
   considerations from it also apply to this document.















































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<span class="h2"><a class="selflink" name="section-5" href="#section-5">5</a>.  IANA Considerations</span>

   There is no new IANA considerations in this document.
















































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<span class="h2"><a class="selflink" name="section-6" href="#section-6">6</a>.  Acknowledgements</span>

   Most of the contents of this document is copied from the <a href="./rfc5996">RFC 5996</a>.
















































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<span class="h2"><a class="selflink" name="section-7" href="#section-7">7</a>.  References</span>

<span class="h3"><a class="selflink" name="section-7.1" href="#section-7.1">7.1</a>.  Normative References</span>

   [<a name="ref-RFC2119" id="ref-RFC2119">RFC2119</a>]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", <a href="./bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.

   [<a name="ref-RFC5996" id="ref-RFC5996">RFC5996</a>]  Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
              "Internet Key Exchange Protocol Version 2 (IKEv2)",
              <a href="./rfc5996">RFC 5996</a>, September 2010.

<span class="h3"><a class="selflink" name="section-7.2" href="#section-7.2">7.2</a>.  Informative References</span>

   [<a name="ref-IKEV2IANA" id="ref-IKEV2IANA">IKEV2IANA</a>]
              "Internet Key Exchange Version 2 (IKEv2) Parameters",
              &lt;<a href="http://www.iana.org">http://www.iana.org</a>&gt;.

   [<a name="ref-MODES" id="ref-MODES">MODES</a>]    National Institute of Standards and Technology, U.S.
              Department of Commerce, "Recommendation for Block Cipher
              Modes of Operation", SP 800-38A, 2001.

   [<a name="ref-RFC3447" id="ref-RFC3447">RFC3447</a>]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography
              Standards (PKCS) #1: RSA Cryptography Specifications
              Version 2.1", <a href="./rfc3447">RFC 3447</a>, February 2003.

   [<a name="ref-RFC5280" id="ref-RFC5280">RFC5280</a>]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", <a href="./rfc5280">RFC 5280</a>, May 2008.

   [<a name="ref-RSA" id="ref-RSA">RSA</a>]      R. Rivest, A. Shamir, and L. Adleman, "A Method for
              Obtaining Digital Signatures and Public-Key
              Cryptosystems", February 1978.


















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<span class="h2"><a class="selflink" name="appendix-A" href="#appendix-A">Appendix A</a>.  Header and Payload Formats</span>

   This appendix describes actual packet payload formats.  This is
   required to make the document self contained.  The descriptions are
   mostly copied from the <a href="./rfc5996">RFC5996</a> and more information can be found from
   there.

   Various payload contains RESERVED fields and those MUST be sent as
   zero and MUST be ignored on receipt.

   All multi-octet fields representing integers are laid out in big
   endian order (also known as "most significant byte first", or
   "network byte order").

<span class="h1"><a class="selflink" name="appendix-A.1" href="#appendix-A.1">A.1</a>.  The IKE Header</span>

   Each IKEv2 message begins with the IKE header, denoted HDR in this
   document.  Following the header are one or more IKE payloads each
   identified by a "Next Payload" field in the preceding payload.
   Payloads are identified in the order in which they appear in an IKE
   message by looking in the "Next Payload" field in the IKE header, and
   subsequently according to the "Next Payload" field in the IKE payload
   itself until a "Next Payload" field of zero indicates that no
   payloads follow.  If a payload of type "Encrypted" is found, that
   payload is decrypted and its contents parsed as additional payloads.
   An Encrypted payload MUST be the last payload in a packet and an
   Encrypted payload MUST NOT contain another Encrypted payload.

   The format of the IKE header is shown in Figure 1.

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       IKE SA Initiator's SPI                  |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       IKE SA Responder's SPI                  |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Next Payload | MjVer | MnVer | Exchange Type |     Flags     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Message ID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Length                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 1:  IKE Header Format




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   o  Initiator's SPI (8 octets) - A value chosen by the initiator to
      identify a unique IKE Security Association.  This value MUST NOT
      be zero.

   o  Responder's SPI (8 octets) - A value chosen by the responder to
      identify a unique IKE Security Association.  This value MUST be
      zero in the first message of an IKE initial exchange.

   o  Next Payload (1 octet) - Indicates the type of payload that
      immediately follows the header.  The format and value of each
      payload are defined below.

   o  Major Version (4 bits) - Indicates the major version of the IKE
      protocol in use.  Implementations based on this version of IKE
      MUST set the major version to 2 and MUST drop the messages with a
      higher major version number.

   o  Minor Version (4 bits) - Indicates the minor version of the IKE
      protocol in use.  Implementations based on this version of IKE
      MUST set the minor version to 0.  They MUST ignore the minor
      version number of received messages.

   o  Exchange Type (1 octet) - Indicates the type of exchange being
      used.  This constrains the payloads sent in each message in an
      exchange.

      Exchange Type             Value
      ----------------------------------
      IKE_SA_INIT               34
      IKE_AUTH                  35
      CREATE_CHILD_SA           36
      INFORMATIONAL             37

   o  Flags (1 octet) - Indicates specific options that are set for the
      message.  Presence of options is indicated by the appropriate bit
      in the flags field being set.  The bits are as follows:

        +-+-+-+-+-+-+-+-+
        |X|X|R|V|I|X|X|X|
        +-+-+-+-+-+-+-+-+

      In the description below, a bit being 'set' means its value is
      '1', while 'cleared' means its value is '0'.  'X' bits MUST be
      cleared when sending and MUST be ignored on receipt.

      *  R (Response) - This bit indicates that this message is a
         response to a message containing the same Message ID.  This bit
         MUST be cleared in all request messages and MUST be set in all



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         responses.  An IKEv2 endpoint MUST NOT generate a response to a
         message that is marked as being a response.

      *  V (Version) - This bit indicates that the transmitter is
         capable of speaking a higher major version number of the
         protocol than the one indicated in the major version number
         field.  Implementations of IKEv2 MUST clear this bit when
         sending and MUST ignore it in incoming messages.

      *  I (Initiator) - This bit MUST be set in messages sent by the
         original initiator of the IKE SA and MUST be cleared in
         messages sent by the original responder.  It is used by the
         recipient to determine which eight octets of the SPI were
         generated by the recipient.  This bit changes to reflect who
         initiated the last rekey of the IKE SA.

   o  Message ID (4 octets, unsigned integer) - Message identifier used
      to control retransmission of lost packets and matching of requests
      and responses.  It is essential to the security of the protocol
      because it is used to prevent message replay attacks.

   o  Length (4 octets, unsigned integer) - Length of the total message
      (header + payloads) in octets.

<span class="h1"><a class="selflink" name="appendix-A.2" href="#appendix-A.2">A.2</a>.  Generic Payload Header</span>

   Each IKE payload begins with a generic payload header, shown in
   Figure 2.  Figures for each payload below will include the generic
   payload header, but for brevity, the description of each field will
   be omitted.

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 2:  Generic Payload Header

   The Generic Payload Header fields are defined as follows:

   o  Next Payload (1 octet) - Identifier for the payload type of the
      next payload in the message.  If the current payload is the last
      in the message, then this field will be 0.  This field provides a
      "chaining" capability whereby additional payloads can be added to
      a message by appending each one to the end of the message and
      setting the "Next Payload" field of the preceding payload to
      indicate the new payload's type.  An Encrypted payload, which must



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      always be the last payload of a message, is an exception.  It
      contains data structures in the format of additional payloads.  In
      the header of an Encrypted payload, the Next Payload field is set
      to the payload type of the first contained payload (instead of 0);
      conversely, the Next Payload field of the last contained payload
      is set to zero).  The payload type values needed for minimal
      implementations are listed here.

      Next Payload Type                Notation  Value
      --------------------------------------------------
      No Next Payload                             0
      Security Association             SA         33
      Key Exchange                     KE         34
      Identification - Initiator       IDi        35
      Identification - Responder       IDr        36
      Certificate                      CERT       37
      Certificate Request              CERTREQ    38
      Authentication                   AUTH       39
      Nonce                            Ni, Nr     40
      Notify                           N          41
      Delete                           D          42
      Traffic Selector - Initiator     TSi        44
      Traffic Selector - Responder     TSr        45
      Encrypted and Authenticated      SK         46

   o  Critical (1 bit) - MUST be set to zero if the sender wants the
      recipient to skip this payload if it does not understand the
      payload type code in the Next Payload field of the previous
      payload.  MUST be set to one if the sender wants the recipient to
      reject this entire message if it does not understand the payload
      type.  MUST be ignored by the recipient if the recipient
      understands the payload type code.  MUST be set to zero for
      payload types defined in this document.  Note that the critical
      bit applies to the current payload rather than the "next" payload
      whose type code appears in the first octet.

   o  Payload Length (2 octets, unsigned integer) - Length in octets of
      the current payload, including the generic payload header.

<span class="h1"><a class="selflink" name="appendix-A.3" href="#appendix-A.3">A.3</a>.  Security Association Payload</span>

   The Security Association payload, denoted SA in this document, is
   used to negotiate attributes of a Security Association.

   An SA payload consists of one or more proposals.  Each proposal
   includes one protocol.  Each protocol contains one or more transforms
   -- each specifying a cryptographic algorithm.  Each transform
   contains zero or more attributes (attributes are needed only if the



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   Transform ID does not completely specify the cryptographic algorithm,
   currently only attribute is key length attribute for variable length
   ciphers, meaning there is exactly zero or one attribute).

   The responder MUST choose a single suite, which may be any subset of
   the SA proposal following the rules below.

   Each proposal contains one protocol.  If a proposal is accepted, the
   SA response MUST contain the same protocol.  Each IPsec protocol
   proposal contains one or more transforms.  Each transform contains a
   Transform Type.  The accepted cryptographic suite MUST contain
   exactly one transform of each type included in the proposal.  For
   example: if an ESP proposal includes transforms ENCR_3DES, ENCR_AES
   w/keysize 128, ENCR_AES w/keysize 256, AUTH_HMAC_MD5, and
   AUTH_HMAC_SHA, the accepted suite MUST contain one of the ENCR_
   transforms and one of the AUTH_ transforms.  Thus, six combinations
   are acceptable.

   Minimal implementation can create very simple SA proposal, i.e.
   include one proposal, which contains exactly one transform for each
   transform type.  It is important to only include one Diffie-Hellman
   group in proposal, so there is no need to do INVALID_KE_PAYLOAD
   processing in responses.

   When parsing an SA, an implementation MUST check that the total
   Payload Length is consistent with the payload's internal lengths and
   counts.  Proposals, Transforms, and Attributes each have their own
   variable-length encodings.  They are nested such that the Payload
   Length of an SA includes the combined contents of the SA, Proposal,
   Transform, and Attribute information.  The length of a Proposal
   includes the lengths of all Transforms and Attributes it contains.
   The length of a Transform includes the lengths of all Attributes it
   contains.

   Each Proposal/Protocol structure is followed by one or more transform
   structures.  The number of different transforms is generally
   determined by the Protocol.  AH generally has two transforms:
   Extended Sequence Numbers (ESNs) and an integrity check algorithm.
   ESP generally has three: ESN, an encryption algorithm, and an
   integrity check algorithm.  IKEv2 generally has four transforms: a
   Diffie-Hellman group, an integrity check algorithm, a PRF algorithm,
   and an encryption algorithm.  For each Protocol, the set of
   permissible transforms is assigned Transform ID numbers, which appear
   in the header of each transform.

   If there are multiple transforms with the same Transform Type, the
   proposal is an OR of those transforms.  If there are multiple
   transforms with different Transform Types, the proposal is an AND of



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   the different groups.

   A given transform MAY have one or more Attributes.  Attributes are
   necessary when the transform can be used in more than one way, as
   when an encryption algorithm has a variable key size.  The transform
   would specify the algorithm and the attribute would specify the key
   size.  To propose alternate values for an attribute (for example,
   multiple key sizes for the AES encryption algorithm), an
   implementation MUST include multiple transforms with the same
   Transform Type each with a single Attribute.

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                          &lt;Proposals&gt;                          ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 3:  Security Association Payload

   o  Proposals (variable) - One or more proposal substructures.

<span class="h1"><a class="selflink" name="appendix-A.3.1" href="#appendix-A.3.1">A.3.1</a>.  Proposal Substructure</span>

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 0 (last) or 2 |   RESERVED    |         Proposal Length       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Proposal Num  |  Protocol ID  |    SPI Size   |Num  Transforms|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                        SPI (variable)                         ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                        &lt;Transforms&gt;                           ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 4:  Proposal Substructure

   o  0 (last) or 2 (more) (1 octet) - Specifies whether this is the
      last Proposal Substructure in the SA.

   o  Proposal Length (2 octets, unsigned integer) - Length of this
      proposal, including all transforms and attributes that follow.



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   o  Proposal Num (1 octet) - When a proposal is made, the first
      proposal in an SA payload MUST be 1, and subsequent proposals MUST
      be one more than the previous proposal.  When a proposal is
      accepted, the proposal number in the SA payload MUST match the
      number on the proposal sent that was accepted.

   o  Protocol ID (1 octet) - Specifies the IPsec protocol identifier
      for the current negotiation.

      Protocol                Protocol ID
      -----------------------------------
      IKE                     1
      AH                      2
      ESP                     3

   o  SPI Size (1 octet) - For an initial IKE SA negotiation, this field
      MUST be zero; the SPI is obtained from the outer header.  During
      subsequent negotiations, it is equal to the size, in octets, of
      the SPI of the corresponding protocol (8 for IKE, 4 for ESP and
      AH).

   o  Num Transforms (1 octet) - Specifies the number of transforms in
      this proposal.

   o  SPI (variable) - The sending entity's SPI.  When the SPI Size
      field is zero, this field is not present in the Security
      Association payload.

   o  Transforms (variable) - One or more transform substructures.

<span class="h1"><a class="selflink" name="appendix-A.3.2" href="#appendix-A.3.2">A.3.2</a>.  Transform Substructure</span>

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 0 (last) or 3 |   RESERVED    |        Transform Length       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Transform Type |   RESERVED    |          Transform ID         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                      Transform Attributes                     ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 5:  Transform Substructure






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   o  0 (last) or 3 (more) (1 octet) - Specifies whether this is the
      last Transform Substructure in the Proposal.

   o  Transform Length - The length (in octets) of the Transform
      Substructure including Header and Attributes.

   o  Transform Type (1 octet) - The type of transform being specified
      in this transform.  Different protocols support different
      Transform Types.  For some protocols, some of the transforms may
      be optional.  If a transform is optional and the initiator wishes
      to propose that the transform be omitted, no transform of the
      given type is included in the proposal.  If the initiator wishes
      to make use of the transform optional to the responder, it
      includes a transform substructure with Transform ID = 0 as one of
      the options.

   o  Transform ID (2 octets) - The specific instance of the Transform
      Type being proposed.

   The relevant Transform Type values are listed below.

   Description                     Trans.  Used In
                                   Type
   ------------------------------------------------------------------
   Encryption Algorithm (ENCR)     1       IKE and ESP
   Pseudorandom Function (PRF)     2       IKE
   Integrity Algorithm (INTEG)     3       IKE, AH, optional in ESP
   Diffie-Hellman group (D-H)      4       IKE, optional in AH &amp; ESP
   Extended Sequence Numbers (ESN) 5       AH and ESP

   For Transform Type 1 (Encryption Algorithm), the relevant Transform
   IDs are listed below.

   Name                 Number      Defined In
   ---------------------------------------------------
   ENCR_3DES            3           (<a href="./rfc2451">RFC2451</a>)
   ENCR_AES_CBC         12          (<a href="./rfc3602">RFC3602</a>)

   For Transform Type 2 (Pseudorandom Function), the relevant Transform
   IDs are listed below.

   Name                        Number    Defined In
   ------------------------------------------------------
   PRF_HMAC_MD5                1         (<a href="./rfc2104">RFC2104</a>), [MD5]
   PRF_HMAC_SHA1               2         (<a href="./rfc2104">RFC2104</a>), [SHA]

   For Transform Type 3 (Integrity Algorithm), relevant Transform IDs
   are listed below.



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   Name                 Number   Defined In
   ----------------------------------------
   NONE                 0
   AUTH_HMAC_MD5_96     1        (<a href="./rfc2403">RFC2403</a>)
   AUTH_HMAC_SHA1_96    2        (<a href="./rfc2404">RFC2404</a>)
   AUTH_AES_XCBC_96     5        (<a href="./rfc3566">RFC3566</a>)

   For Transform Type 4 (Diffie-Hellman group), relevant Transform IDs
   are listed below.

   Name               Number     Defined In
   ----------------------------------------
   NONE               0
   768-bit MODP       1          <a href="#appendix-B">Appendix B</a>
   1024-bit MODP      2          <a href="#appendix-B">Appendix B</a>
   1536-bit MODP      5          [ADDGROUP]
   2048-bit MODP      14         [ADDGROUP]

   For Transform Type 5 (Extended Sequence Numbers), relevant Transform
   IDs are listed below.

   Name                               Number
   --------------------------------------------
   No Extended Sequence Numbers       0
   Extended Sequence Numbers          1

   Note that an initiator who supports ESNs will usually include two ESN
   transforms, with values "0" and "1", in its proposals.  A proposal
   containing a single ESN transform with value "1" means that using
   normal (non-extended) sequence numbers is not acceptable.

<span class="h1"><a class="selflink" name="appendix-A.3.3" href="#appendix-A.3.3">A.3.3</a>.  Valid Transform Types by Protocol</span>

   The number and type of transforms that accompany an SA payload are
   dependent on the protocol in the SA itself.  An SA payload proposing
   the establishment of an SA has the following mandatory and optional
   Transform Types.  A compliant implementation MUST understand all
   mandatory and optional types for each protocol it supports (though it
   need not accept proposals with unacceptable suites).  A proposal MAY
   omit the optional types if the only value for them it will accept is
   NONE.

   Protocol    Mandatory Types          Optional Types
   ---------------------------------------------------
   IKE         ENCR, PRF, INTEG, D-H
   ESP         ENCR, ESN                INTEG, D-H
   AH          INTEG, ESN               D-H




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<span class="h1"><a class="selflink" name="appendix-A.3.4" href="#appendix-A.3.4">A.3.4</a>.  Transform Attributes</span>

   Transform type 1 (Encryption Algorithm) transforms might include one
   transform attribute: Key Length.

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |1|       Attribute Type        |        Attribute Value        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   Figure 6:  Data Attributes

   o  Attribute Type (15 bits) - Unique identifier for each type of
      attribute (see below).

   o  Attribute Value - Value of the attribute associated with the
      attribute type.


   Attribute Type         Value
   ----------------------------
   Key Length (in bits)   14

   The Key Length attribute specifies the key length in bits (MUST use
   network byte order) for certain transforms as follows:

   o  The Key Length attribute MUST NOT be used with transforms that use
      a fixed-length key.

   o  Some transforms specify that the Key Length attribute MUST be
      always included.  For example ENCR_AES_CBC.

<span class="h1"><a class="selflink" name="appendix-A.4" href="#appendix-A.4">A.4</a>.  Key Exchange Payload</span>

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Diffie-Hellman Group Num    |           RESERVED            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                       Key Exchange Data                       ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 7:  Key Exchange Payload Format




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   A Key Exchange payload is constructed by copying one's Diffie-Hellman
   public value into the "Key Exchange Data" portion of the payload.
   The length of the Diffie-Hellman public value for modular
   exponentiation group (MODP) groups MUST be equal to the length of the
   prime modulus over which the exponentiation was performed, prepending
   zero bits to the value if necessary.

   The Diffie-Hellman Group Num identifies the Diffie-Hellman group in
   which the Key Exchange Data was computed.  This Diffie-Hellman Group
   Num MUST match a Diffie-Hellman group specified in a proposal in the
   SA payload that is sent in the same message

<span class="h1"><a class="selflink" name="appendix-A.5" href="#appendix-A.5">A.5</a>.  Identification Payloads</span>

   The Identification payloads, denoted IDi and IDr in this document,
   allow peers to assert an identity to one another.  When using the
   ID_IPV4_ADDR/ID_IPV6_ADDR identity types in IDi/IDr payloads, IKEv2
   does not require this address to match the address in the IP header
   of IKEv2 packets, or anything in the TSi/TSr payloads.  The contents
   of IDi/IDr are used purely to fetch the policy and authentication
   data related to the other party.  In minimal implementation it might
   be easiest to always use KEY_ID type.  This allows the ID payload to
   be static.  Using IP address has problems in environments where IP
   addresses are dynamically allocated.

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   ID Type     |                 RESERVED                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                   Identification Data                         ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 8:  Identification Payload Format

   o  ID Type (1 octet) - Specifies the type of Identification being
      used.

   o  Identification Data (variable length) - Value, as indicated by the
      Identification Type.  The length of the Identification Data is
      computed from the size in the ID payload header.

   The following table lists the assigned semantics for the
   Identification Type field.



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   ID Type                           Value
   -------------------------------------------------------------------
   ID_IPV4_ADDR                        1
      A single four (4) octet IPv4 address.

   ID_FQDN                             2
      A fully-qualified domain name string.  An example of an ID_FQDN
      is "example.com".  The string MUST NOT contain any terminators
      (e.g., NULL, CR, etc.). All characters in the ID_FQDN are ASCII;
      for an "internationalized domain name", the syntax is as defined
      in [IDNA], for example "xn--tmonesimerkki-bfbb.example.net".

   ID_RFC822_ADDR                      3
      A fully-qualified <a href="./rfc822">RFC 822</a> email address string.  An example of a
      ID_RFC822_ADDR is "jsmith@example.com".  The string MUST NOT
      contain any terminators.  Because of [EAI], implementations would
      be wise to treat this field as UTF-8 encoded text, not as
      pure ASCII.

   ID_IPV6_ADDR                        5
      A single sixteen (16) octet IPv6 address.

   ID_KEY_ID                           11
      An opaque octet stream that may be used to pass vendor-
      specific information necessary to do certain proprietary
      types of identification. Minimal implementation might use
      this type to send out serial number or similar device
      specific unique static identification data for the device.

<span class="h1"><a class="selflink" name="appendix-A.6" href="#appendix-A.6">A.6</a>.  Certificate Payload</span>

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Cert Encoding |                                               |
   +-+-+-+-+-+-+-+-+                                               |
   ~                       Certificate Data                        ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 9:  Certificate Payload Format

   o  Certificate Encoding (1 octet) - This field indicates the type of
      certificate or certificate-related information contained in the
      Certificate Data field.




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      Certificate Encoding                 Value
      ----------------------------------------------------
      X.509 Certificate - Signature        4
      Raw RSA Key                          11

   o  Certificate Data (variable length) - Actual encoding of
      certificate data.  The type of certificate is indicated by the
      Certificate Encoding field.

   The syntax of the types above are:

   o  "X.509 Certificate - Signature" contains a DER-encoded X.509
      certificate whose public key is used to validate the sender's AUTH
      payload.  Note that with this encoding, if a chain of certificates
      needs to be sent, multiple CERT payloads are used, only the first
      of which holds the public key used to validate the sender's AUTH
      payload.

   o  "Raw RSA Key" contains a PKCS #1 encoded RSA key, that is, a DER-
      encoded RSAPublicKey structure (see [<a href="#ref-RSA" title="&quot;A Method for Obtaining Digital Signatures and Public-Key Cryptosystems&quot;">RSA</a>] and [<a href="./rfc3447" title="&quot;Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1&quot;">RFC3447</a>]).

<span class="h1"><a class="selflink" name="appendix-A.7" href="#appendix-A.7">A.7</a>.  Certificate Request Payload</span>

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Cert Encoding |                                               |
   +-+-+-+-+-+-+-+-+                                               |
   ~                    Certification Authority                    ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 10:  Certificate Request Payload Format

   o  Certificate Encoding (1 octet) - Contains an encoding of the type
      or format of certificate requested.

   o  Certification Authority (variable length) - Contains an encoding
      of an acceptable certification authority for the type of
      certificate requested.

   The Certificate Encoding field has the same values as those defined
   certificate payload.  The Certification Authority field contains an
   indicator of trusted authorities for this certificate type.  The
   Certification Authority value is a concatenated list of SHA-1 hashes
   of the public keys of trusted Certification Authorities (CAs).  Each



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   is encoded as the SHA-1 hash of the Subject Public Key Info element
   (see <a href="./rfc5280#section-4.1.2.7">section&nbsp;4.1.2.7 of [RFC5280]</a>) from each Trust Anchor
   certificate.  The 20-octet hashes are concatenated and included with
   no other formatting.

<span class="h1"><a class="selflink" name="appendix-A.8" href="#appendix-A.8">A.8</a>.  Authentication Payload</span>

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Auth Method   |                RESERVED                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                      Authentication Data                      ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 11:  Authentication Payload Format

   o  Auth Method (1 octet) - Specifies the method of authentication
      used.

   Mechanism                              Value
   -----------------------------------------------------------------
   RSA Digital Signature                  1
      Using an RSA private key with RSASSA-PKCS1-v1_5 signature
      scheme specified in [PKCS1], see <a href="./rfc5996#section-2.15">[RFC5996] section&nbsp;2.15</a> for
      details.

   Shared Key Message Integrity Code      2
      Computed as specified earlier using the shared key associated
      with the identity in the ID payload and the negotiated PRF.

   DSS Digital Signature                  3
      Using a DSS private key (see [DSS]) over a SHA-1 hash, see
      <a href="./rfc5996#section-2.15">[RFC5996] Section&nbsp;2.15</a> for details.

   o  Authentication Data (variable length) - see <a href="#section-2.1">Section 2.1</a>.











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<span class="h1"><a class="selflink" name="appendix-A.9" href="#appendix-A.9">A.9</a>.  Nonce Payload</span>

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                            Nonce Data                         ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 12:  Nonce Payload Format

   o  Nonce Data (variable length) - Contains the random data generated
      by the transmitting entity.

   The size of the Nonce Data MUST be between 16 and 256 octets,
   inclusive.  Nonce values MUST NOT be reused.

<span class="h1"><a class="selflink" name="appendix-A.10" href="#appendix-A.10">A.10</a>.  Notify Payload</span>

   The Notify payload, denoted N in this document, is used to transmit
   informational data, such as error conditions and state transitions,
   to an IKE peer.  A Notify payload may appear in a response message
   (usually specifying why a request was rejected), in an INFORMATIONAL
   Exchange (to report an error not in an IKE request), or in any other
   message to indicate sender capabilities or to modify the meaning of
   the request.

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Protocol ID  |   SPI Size    |      Notify Message Type      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                Security Parameter Index (SPI)                 ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                       Notification Data                       ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 13:  Notify Payload Format




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   o  Protocol ID (1 octet) - If this notification concerns an existing
      SA whose SPI is given in the SPI field, this field indicates the
      type of that SA.  If the SPI field is empty, this field MUST be
      sent as zero and MUST be ignored on receipt.

   o  SPI Size (1 octet) - Length in octets of the SPI as defined by the
      IPsec protocol ID or zero if no SPI is applicable.  For a
      notification concerning the IKE SA, the SPI Size MUST be zero and
      the field must be empty.

   o  Notify Message Type (2 octets) - Specifies the type of
      notification message.

   o  SPI (variable length) - Security Parameter Index.

   o  Notification Data (variable length) - Status or error data
      transmitted in addition to the Notify Message Type.  Values for
      this field are type specific.

<span class="h1"><a class="selflink" name="appendix-A.10.1" href="#appendix-A.10.1">A.10.1</a>.  Notify Message Types</span>

   Notification information can be error messages specifying why an SA
   could not be established.  It can also be status data that a process
   managing an SA database wishes to communicate with a peer process.

   Types in the range 0 - 16383 are intended for reporting errors.  An
   implementation receiving a Notify payload with one of these types
   that it does not recognize in a response MUST assume that the
   corresponding request has failed entirely.  Unrecognized error types
   in a request and status types in a request or response MUST be
   ignored, and they should be logged.

   Notify payloads with status types MAY be added to any message and
   MUST be ignored if not recognized.  They are intended to indicate
   capabilities, and as part of SA negotiation, are used to negotiate
   non-cryptographic parameters.















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   NOTIFY messages: error types              Value
   -------------------------------------------------------------------
   UNSUPPORTED_CRITICAL_PAYLOAD              1
       Indicates that the one-octet payload type included in the
       Notification Data field is unknown.

   INVALID_SYNTAX                            7
       Indicates the IKE message that was received was invalid because
       some type, length, or value was out of range or because the
       request was rejected for policy reasons.  To avoid a DoS
       attack using forged messages, this status may only be
       returned for and in an encrypted packet if the Message ID and
       cryptographic checksum were valid.  To avoid leaking information
       to someone probing a node, this status MUST be sent in response
       to any error not covered by one of the other status types.
       To aid debugging, more detailed error information should be
       written to a console or log.

   NO_PROPOSAL_CHOSEN                       14
       None of the proposed crypto suites was acceptable.  This can be
       sent in any case where the offered proposals are not acceptable
       for the responder.

   NO_ADDITIONAL_SAS                        35
       Specifies that the node is unwilling to accept any more Child
       SAs.



   NOTIFY messages: status types            Value
   -------------------------------------------------------------------
   INITIAL_CONTACT                          16384
       Asserts that this IKE SA is the only IKE SA currently active
       between the authenticated identities.


<span class="h1"><a class="selflink" name="appendix-A.11" href="#appendix-A.11">A.11</a>.  Traffic Selector Payload</span>

   Traffic Selector (TS) payloads allow endpoints to communicate some of
   the information from their SPD to their peers.  TS payloads specify
   the selection criteria for packets that will be forwarded over the
   newly set up SA.









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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Number of TSs |                 RESERVED                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                       &lt;Traffic Selectors&gt;                     ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 14:  Traffic Selectors Payload Format

   o  Number of TSs (1 octet) - Number of Traffic Selectors being
      provided.

   o  Traffic Selectors (variable length) - One or more individual
      Traffic Selectors.

   The length of the Traffic Selector payload includes the TS header and
   all the Traffic Selectors.

   There is no requirement that TSi and TSr contain the same number of
   individual Traffic Selectors.  Thus, they are interpreted as follows:
   a packet matches a given TSi/TSr if it matches at least one of the
   individual selectors in TSi, and at least one of the individual
   selectors in TSr.

   Two TS payloads appear in each of the messages in the exchange that
   creates a Child SA pair.  Each TS payload contains one or more
   Traffic Selectors.  Each Traffic Selector consists of an address
   range (IPv4 or IPv6), a port range, and an IP protocol ID.

   The first of the two TS payloads is known as TSi (Traffic Selector-
   initiator).  The second is known as TSr (Traffic Selector-responder).
   TSi specifies the source address of traffic forwarded from (or the
   destination address of traffic forwarded to) the initiator of the
   Child SA pair.  TSr specifies the destination address of the traffic
   forwarded to (or the source address of the traffic forwarded from)
   the responder of the Child SA pair.

   IKEv2 allows the responder to choose a subset of the traffic proposed
   by the initiator.

   When the responder chooses a subset of the traffic proposed by the
   initiator, it narrows the Traffic Selectors to some subset of the
   initiator's proposal (provided the set does not become the null set).



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   If the type of Traffic Selector proposed is unknown, the responder
   ignores that Traffic Selector, so that the unknown type is not
   returned in the narrowed set.

   To enable the responder to choose the appropriate range, if the
   initiator has requested the SA due to a data packet, the initiator
   SHOULD include as the first Traffic Selector in each of TSi and TSr a
   very specific Traffic Selector including the addresses in the packet
   triggering the request.  If the initiator creates the Child SA pair
   not in response to an arriving packet, but rather, say, upon startup,
   then there may be no specific addresses the initiator prefers for the
   initial tunnel over any other.  In that case, the first values in TSi
   and TSr can be ranges rather than specific values.

   As minimal implementations might only support one SA, the traffic
   selectors will usually be from initiator's IP address to responders
   IP address (i.e. no port or protocol selectors and only one range).

<span class="h1"><a class="selflink" name="appendix-A.11.1" href="#appendix-A.11.1">A.11.1</a>.  Traffic Selector</span>

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   TS Type     |IP Protocol ID |       Selector Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Start Port          |           End Port            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                         Starting Address                      ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                         Ending Address                        ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 15: Traffic Selector

   o  TS Type (one octet) - Specifies the type of Traffic Selector.

   o  IP protocol ID (1 octet) - Value specifying an associated IP
      protocol ID (such as UDP, TCP, and ICMP).  A value of zero means
      that the protocol ID is not relevant to this Traffic Selector --
      the SA can carry all protocols.

   o  Selector Length - Specifies the length of this Traffic Selector
      substructure including the header.




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   o  Start Port (2 octets, unsigned integer) - Value specifying the
      smallest port number allowed by this Traffic Selector.  For
      protocols for which port is undefined (including protocol 0), or
      if all ports are allowed, this field MUST be zero.

   o  End Port (2 octets, unsigned integer) - Value specifying the
      largest port number allowed by this Traffic Selector.  For
      protocols for which port is undefined (including protocol 0), or
      if all ports are allowed, this field MUST be 65535.

   o  Starting Address - The smallest address included in this Traffic
      Selector (length determined by TS Type).

   o  Ending Address - The largest address included in this Traffic
      Selector (length determined by TS Type).

   The following table lists values for the Traffic Selector Type field
   and the corresponding Address Selector Data.

   TS Type                            Value
   -------------------------------------------------------------------
   TS_IPV4_ADDR_RANGE                  7

       A range of IPv4 addresses, represented by two four-octet
       values.  The first value is the beginning IPv4 address
       (inclusive) and the second value is the ending IPv4 address
       (inclusive).  All addresses falling between the two specified
       addresses are considered to be within the list.

   TS_IPV6_ADDR_RANGE                  8

       A range of IPv6 addresses, represented by two sixteen-octet
       values.  The first value is the beginning IPv6 address
       (inclusive) and the second value is the ending IPv6 address
       (inclusive).  All addresses falling between the two specified
       addresses are considered to be within the list.

<span class="h1"><a class="selflink" name="appendix-A.12" href="#appendix-A.12">A.12</a>.  Encrypted Payload</span>

   The Encrypted payload, denoted SK{...} in this document, contains
   other payloads in encrypted form.










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                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Initialization Vector                     |
   |         (length is block size for encryption algorithm)       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                    Encrypted IKE Payloads                     ~
   +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               |             Padding (0-255 octets)            |
   +-+-+-+-+-+-+-+-+                               +-+-+-+-+-+-+-+-+
   |                                               |  Pad Length   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                    Integrity Checksum Data                    ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 16:  Encrypted Payload Format

   o  Next Payload - The payload type of the first embedded payload.
      Note that this is an exception in the standard header format,
      since the Encrypted payload is the last payload in the message and
      therefore the Next Payload field would normally be zero.  But
      because the content of this payload is embedded payloads and there
      was no natural place to put the type of the first one, that type
      is placed here.

   o  Payload Length - Includes the lengths of the header,
      initialization vector (IV), Encrypted IKE payloads, Padding, Pad
      Length, and Integrity Checksum Data.

   o  Initialization Vector - For CBC mode ciphers, the length of the
      initialization vector (IV) is equal to the block length of the
      underlying encryption algorithm.  Senders MUST select a new
      unpredictable IV for every message; recipients MUST accept any
      value.  The reader is encouraged to consult [<a href="#ref-MODES" title="&quot;Recommendation for Block Cipher Modes of Operation&quot;">MODES</a>] for advice on
      IV generation.  In particular, using the final ciphertext block of
      the previous message is not considered unpredictable.  For modes
      other than CBC, the IV format and processing is specified in the
      document specifying the encryption algorithm and mode.

   o  IKE payloads are as specified earlier in this section.  This field
      is encrypted with the negotiated cipher.

   o  Padding MAY contain any value chosen by the sender, and MUST have
      a length that makes the combination of the payloads, the Padding,
      and the Pad Length to be a multiple of the encryption block size.
      This field is encrypted with the negotiated cipher.



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   o  Pad Length is the length of the Padding field.  The sender SHOULD
      set the Pad Length to the minimum value that makes the combination
      of the payloads, the Padding, and the Pad Length a multiple of the
      block size, but the recipient MUST accept any length that results
      in proper alignment.  This field is encrypted with the negotiated
      cipher.

   o  Integrity Checksum Data is the cryptographic checksum of the
      entire message starting with the Fixed IKE header through the Pad
      Length.  The checksum MUST be computed over the encrypted message.
      Its length is determined by the integrity algorithm negotiated.








































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<span class="h2"><a class="selflink" name="appendix-B" href="#appendix-B">Appendix B</a>.  Useful Optional Features</span>

   There are some optional features of IKEv2, which might be useful for
   minimal implementations in some scenarios.  Such features include Raw
   RSA keys authentication, and sending IKE SA delete notification.

<span class="h1"><a class="selflink" name="appendix-B.1" href="#appendix-B.1">B.1</a>.  IKE SA Delete Notification</span>

   In some scenarios the minimal implementation device creates IKE SA,
   sends one or few packets, perhaps gets some packets back, and then
   device goes back to sleep forgetting the IKE SA.  In such scenarios
   it would be nice for the minimal implementation to send the IKE SA
   delete notification to tell the other end that the IKE SA is going
   away, so it can free the resources.

   Deleting the IKE SA can be done using by sending one packet with
   fixed Message ID, and with only one payload inside the encrypted
   payload.  The other end will send back an empty response:

   Initiator                         Responder
   -------------------------------------------------------------------
   HDR(SPIi=xxx, SPIr=yyy, INFORMATIONAL,
       Flags: Initiator, Message ID=2),
       SK {D}  --&gt;

                      &lt;--  HDR(SPIi=xxx, SPIr=yyy, INFORMATIONAL,
                               Flags: Response, Message ID=2),
                               SK {}

   The delete payload format is:

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Payload  |C|  RESERVED   |         Payload Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Protocol ID   |   SPI Size    |          Num of SPIs          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~               Security Parameter Index(es) (SPI)              ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 17:  Delete Payload Format

   o  Protocol ID (1 octet) - Must be 1 for an IKE SA.





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   o  SPI Size (1 octet) - Length in octets of the SPI as defined by the
      protocol ID.  It MUST be zero for IKE (SPI is in message header).

   o  Num of SPIs (2 octets, unsigned integer) - The number of SPIs
      contained in the Delete payload.  This MUST be zero for IKE.

   o  Security Parameter Index(es) (variable length) - Identifies the
      specific Security Association(s) to delete.  The length of this
      field is determined by the SPI Size and Num of SPIs fields.  This
      field is empty for the IKE SA delete.

<span class="h1"><a class="selflink" name="appendix-B.2" href="#appendix-B.2">B.2</a>.  Raw RSA keys</span>

   In some scenarios the shared secret authentication is not safe
   enough, as anybody who knows the secret can impersonate himself of
   being the server.  If the shared secret is printed on the side of the
   device, then anybody who gets physical access to the device can read
   it.  In such environments public key authentication allows stronger
   authentication with minimal operational overhead.  Certificate
   support is quite complex, and minimal implementations do not usually
   have need for them.  Using Raw RSA keys is much simpler, and it
   allows similar scalability than certificates.  The fingerprint of the
   Raw RSA key can still be distributed by for example printing it on
   the side of the device allowing similar setup than using shared
   secret.

   Raw RSA keys can also be used in leap of faith or baby duck style
   initial setup, where the device imprints itself to the first device
   it sees when it first time boots up.  After that initial connection
   it stores the fingerprint of the Raw RSA key of the server to its own
   configuration and verifies that it never changes (unless reset to
   factory setting or similar command is issued).

   This changes the initial IKE_AUTH payloads as follows:

   Initiator                         Responder
   -------------------------------------------------------------------
   HDR(SPIi=xxx, SPIr=yyy, IKE_AUTH,
       Flags: Initiator, Message ID=1),
       SK {IDi, CERT, AUTH, SAi2, TSi, TSr,
           N(INITIAL_CONTACT)}  --&gt;

                     &lt;--  HDR(SPIi=xxx, SPIr=yyy, IKE_AUTH, Flags:
                                 Response, Message ID=1),
                                 SK {IDr, CERT, AUTH, SAr2, TSi, TSr}

   The CERT payloads contains the Raw RSA keys used the sign the hash of
   the InitiatorSignedOctects/ResponderSignedOctects when generating



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   AUTH payload.  Minimal implementations should use SHA-1 as the hash
   function as that is the SHOULD support algorithm specified in the
   <a href="./rfc5996">RFC5996</a>, so it is the most likely one that is supported by all
   devices.















































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Author's Address

   Tero Kivinen
   AuthenTec
   Eerikinkatu 28
   HELSINKI  FI-00180
   FI

   Email: kivinen@iki.fi










































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